Preparation of Au nanocrosses via a template-directed approach. (a) Schematic illustration of gold nanocross formation based on AuCl₃ reduction by a Cu-based reducing agent. (b) TEM image of the pre-formed Cu nanostructures. (c) TEM image of the as-prepared Au nanocrosses. (d and e) TEM images of a representative Au nanocross with (d) D_2h symmetry and (e) C_2v symmetry. Reproduced from ref. 51 with permission from the Royal Society of Chemistry. (f) UV–vis–NIR absorbance of Au nanocrosses. Reproduced from ref. 50 with permission from American Chemical Society, Copyright 2011. (g) Photothermal stability of gold nanorods upon 980 nm laser irradiation (2 W cm⁻², 30 min). Reproduced from ref. 57 with permission from American Chemical Society, Copyright 2013. (h) TEM image of the palladium nanocollora. Reproduced from ref. 62 with permission from American Chemical Society, Copyright 2011. (i) TEM image of the porous palladium nanoparticles. Reproduced from ref. 63 with permission from the Royal Society of Chemistry.